Means for indicating the residual power capacity of a battery during service



Nov. 12, 1968 SATSURO UMEDA MEANS FOR INDICATING THE RESIDUAL POWERCAPACITY OF A BATTERY DURING SERVICE Filed Dec.

DEC

(BATTERY VOLTAGE LEVEL) IF. (11A) IOO OPERATIVE LIMIT I I ZOKC TUNE+2OKC QESPONSE CURVE ti TAN e= dT Q i TEMP! 0c) INVENTOR.

SATSUQO UMEDA ATTORNEYS United States Patent 3,411,091 MEANS FORINDICATING THE RESIDUAL POWER CAPACITY OF A BATTERY DURING SERVICESatsuro Umeda, 2/332 chome Uehara Shibuya-ku, Tokyo, JapanContinuation-impart of application Ser. No. 250,845, Jan. 11, 1963. Thisapplication Dec. 30, 1966, Ser. No. 606,287 Claims priority, applicationJapan, July 19, 1962, 37/ 29,723 4 Claims. (Cl. 325363) ABSTRACT OF THEDISCLOSURE An ammeter having a reverse temperature compensation due to alarge negative temperature coefficient moving coil magnet, in a batterypowered transistor circuit to olTset the positive temperature dependentvariation in transistor output current such that the maximum currentresponse of the ammeter is an accurate measure of the reserve powerlevel or instantaneous voltage of the battery at all expectedenvironmental temperatures.

The present invention is a continuation-in-part of applicants co-pendingapplication Ser. No. 250,845 filed Jan. 11, 1963, and now abandoned.

The present invention relates to a means for indicating the availablepower capability of a battery during service and more particularly to anammeter means for indicating the residual power level of a battery usedto power a portable transistorized circuit such as a portable radioreceiver.

Because the power output of a battery, for example, a dry cell used asthe power supply of a portable electronic circuit, slowly decreases overa period of time and at a rate dependent on the operating conditions,including such factors as ambient temperature and power drain rate,etc., it becomes difiicult for the circuit user to judge the residualpower level of the battery after it has been in service for a period oftime.

As the power level of, for example, a transistor radio battery dropsoff, the selectivity and sensitivity of the circuit also decrease untilit becomes difficult if not impossible to tune in certain broadcaststations. Further, the final amplifier stage of a transistor radio isusually operated in the Class B mode and if the power level of thebattery drops below a certain operating limit, the plus and minusportions of the push-pull audio wave form are broken otf and the tonequality of any broadcast receptions which are picked up becomes verypoor, if intelligible at all.

For these and other reasons, it is obviously very desirable for the userof a portable electronic circuit such as a transistor radio, to know inadvance about when the battery power supply should be replaced so as toretain the optimum operating conditions of the circuit. The presentinvention was developed and operates to fulfill this specific need.

The present indicating means was specifically designed for use in abattery powered transistor circuit to provide a useful, quantitativeindication of the power capability of the battery. The indicator of thepresent invention also functions, when used in a transistor circuitcapable of being tuned to different signals, to indicate that thecircuit is accurately tuned to one of those signals.

The current variation of a transistor amplifier or converter stage,particularly one controlled by an A.G.C. voltage, is substantial, havinga ratio for the lowest and highest amplitude signals on the order of :1for a strong signal level. The present invention takes advantage ice ofthis amplitude ratio to indicate the decreased transition of the powerlevel of the battery used to power a transistor circuit. A specificallydesigned ammeter having a moving coil, a magnet and a pointer and havinga full scale sensitivity corresponding to the non-signal current valueis connected to be responsive to the output current of an LP. stage of abattery powered transistor circuit.

The output current of the LF. transistor stage has a maximum valuedependent on the power level of the battery during a period while thestage is quiescent, which period occurs in response to no detectablesignal being re ceived because the receiver is not tuned to a station,i.e., the receiver is detuned. The maximum aplitude current causes theammeter pointer to deflect to a maximum quantitative readingcorresponding to the power level of the battery. Thus, the operator canturn on the circuit, tune it away from a signal, and immediately readhow far the power level of the battery has dropped below its rated,shelf value (full scale reading) and determine whether the batteryshould be replaced.

In addition, the design and connection of the ammeter are such that thecurrent fed to the moving coil member reflects the wide current swing ofthe A.G.C. transistor stage as the transistor circuit is tuned to one ofseveral different signals. The ammeter pointer will therefore deflectfrom its maximum, battery power level indicating point to near the zeropoint when a tuning operation is performed. For example, in a transistorradio, the nonsignal, off station current of the A.G.C. transistor stagein which the ammeter is connected may have a value of 400 a. Thatcurrent may decrease sharply to 17 a. when the radio circuit isoptimumly tuned to receive a broadcast frequency. Thus, as the ammeterpointer reverses its deflection with a tuning operation, it is possibleto indicate the tuning center easily and accurately by surveying theminimized current of the A.G.C. transistor stage.

The above noted amplitude factor of a transistor stage varies with theenvironmental temperature due to the effect of the transistors inthecircuit, that is, the temperature dependence which produces avariation in the impedance of a junction transistor; the currentvariations as a function of temperature are defined as a line having apositive slope. For example, in a portable transistor radio carried inan automobile on a hot day, the ambient temperature can increase up to50 C. In such a case, the impedance of a junction transistor in theradio decreases and the quiescent DC. current flow through thetransistor emitter collector path increases. Hence, a conventionalammeter movement connected as indicated above would provide a readingdillerent from the actual battery condition; in the above example themeter would indicate that the battery had a higher power level than itactually had.

The present ammeter indicating means includes a circuit element having anegative temperature coefiicient to provide a reverse temperaturecompensation and thereby oppose the positive transistor temperaturecoefiicient variations. By this means, the ammeter reading is anaccurate representation of the battery power level and the ammeter scalecan be calibrated to accurately determine power level at which thebattery should be replaced.

One object of the invention is to provide an indicating means wherebythe residual capacity of a battery used to power a transistor circuitcan be checked accurately during service.

A second object of the invention is to provide an indicating means whichcan be connected to a transistor circuit without producing a mismatch inthe transistor circuit impedance.

Another object of the invention is to provide an indicating meanswhereby a transistor circuit batterys residual capacity can beaccurately surveyed without interference from the current variations ina temperature dependent junction transistor in the circuit due totemperature gradients affecting the impedance of the transistor.

A still further object of the invention is to provide an indicatingmeans which operates as both a tuning indicator and a battery residualcapacity indicator using ferrite magnets wherever a conventionalelectromagnetic meter instrument can not be used.

The indicating means according to this invention, together withadditional objects and advantages thereof, will be best understood andmore apparent from the following detailed description when read inconnection with the accompanying drawings wherein:

FIG. 1 is a circuit diagram of one form of battery powered transistorcircuit embodying the indicating means of this invention;

FIG. 2 is a. graph showing a non-signal current variation in a junctiontransistor as its impedance varies according to its temperaturedependence;

FIG. 3 is a graph showing the appropriate relations, using aconventional ammeter, of battery voltage to detune transistor outputcurrent according to three different ambient temperature levels;

FIG. 4 is a graph showing the characteristics of the negative currentsensitivity or reverse temperature compensation of the specific meter ofthis invention; and

FIG. 5 is a graph showing the current response curves of an A.G.C.transistor stage through a tuning operating according to differentbattery residual power levels using the specific indicating means ofthis invention.

Referring now to FIG. 1, there is shown a schematic diagram of aportable transistor superheterodyne radio receiver energized by battery11. Power from battery 11 is supplied via switch to, inter alia, theemitter collector paths of NPN transistors 12 and 13, respectivelycomprising the converter and LF. stages of the receiver. Automatic gaincontrol for transistors 12 and 13 is derived by coupling the output ofdetector stage 14, including diode 15, to the bases of transistors 12and 13. The IF amplifying stage 13 provides such a large current gaindue to the A.G.C. voltage control that it is unnecessary to employadditional amplifying circuitry to drive a current responsive meter thatindicates the LF. stage DC. current. The amplitude of the DC. currentfed to the emitter collector path of LF. transistor 13 is dependent,inter alia, on whether tuning circuit 16, connected to converter stage12 is tuned or detuned relative to a broadcast station. As indicated byFIGURE 5, a relatively large DC. current is applied to the collector oftransistor 13 while tuner 16 is detuned from a broadcast station whilethe LF. transistor 13 emitter collector current is relatively low whiletuner 16 is on the center frequency of a broadcast station in proximityto the receiver.

To monitor the DC. current applied to transistor 13 by battery 11, whiletuner 16 is either tuned or detuned relative to a broadcast station,D.C. ammeter 17 is connected in series between battery 11 and theemitter collector path of transistor 13. Meter 17 includes the usualcomponents of moving coil 18, connected to be responsive to the currentflowing into the collector of transistor 13, as well as ferritepermanent magnets 19, core 20 on which coil 18 is wound, angularlydeflectable movement 21, and spring 23 for controlling rotation ofmovement 21. In addition, coil 18 is shunted by resistor 22, having arelatively low negative temperature coefficient, and bypass capacitor 24which substantially decouples any A.C. current from the meter movement.

In use, meter 17 serves the dual function of providing indications ofwhether: (1) battery 11 has a suflicient voltage to enable thetransistors of the receiver to function properly; and (2) tuner 16 isproperly tuned to a broadcast station. The determination of whetherbattery 11 provides sufficient voltage to the circuit is performed byadjusting tuner 16 so that it is detuned from any of the local broadcaststations. If the voltage of battery 11 is insufficient to enabletransistors 12 and 13 to function properly, the movement 21 is deflectedby less than a predetermined angle. Tuner 16 is properly adjusted toreceive a station when movement 21 is deflected to a minimum angle.

However, since the amplitude of DC. current which flows in the IF, stagetransistor 13 varies with the environmental temperature as a functionhaving a positive slope, as shown in FIG. 2, a conventionally designedammeter is inadequate to accurately indicate the current supplied to thecircuit by battery 11. The current drain of the receiver transistors asa function of temperature results in the voltage of battery 11 beinginversely related to temperature, particularly while tuner 16 isdetuned, as clearly shown in FIG. 3 which illustrates the relationbetween the detune current of the transistor stage and the batteryvoltage at three different environmental temperatures A, B and Crepresenting, for example, 25 C., 50 C., and 0 C., respectively. In thecase where the border limit of a battery having a rated, shelf valuecorresponding to a circuit detune current value of 400 ,ua. isapproximately 250 ,ua., curve A provides accurate voltage indications,while curves B and C obviously show indications which respectively arelower and higher than those of the actual battery reserve power levels.A conventional measuring circuit would indicate the temperaturedependent characteristics illustrated by curves B and C and thereby issubject to providing erroneous battery condition indications.

The specific ammeter circuit of this invention has been developed toprovide a battery power level indication which corresponds to curve A ofFIG. 3 at all expected environmental temperatures. To achieve thisresult, the ammeter circuit has a current sensitivity versus temperaturedeflection gradient or slope which opposes the temperature dependentcurrent variations of the transistor stage in which it is connected. Inthe preferred embodiment, shown schematically in FIG. 1 there isconnected in shunt with ammeter coil 18 shunt resistor 22 formed ofcarbon film or the like. Register 18 has an optimum value and a lownegative temperature coeflicient. Magnets 19 of ammeter 17 are formed ofa ferrite material having a large negative temperature coeflicient,whereby the deflection angle of movement 21 versus temperature has aresponse with a negative slope, as illustrated by FIGURE 4.

The graph shown in FIG. 4 illustrates the relation of the deflectionangle of movement 21 to the environmental temperature. The graph showsthat the changing inclination of the sensitivity gradient follows therelation,

where tan 0 is the sensitivity gradient, 0 is the deflection angle, andT is the temperature.

The sensitivity gradient also follows the relation,

tan 0=dildT where z' is a transistor current according to thetemperature T. As seen in FIG. 2, the problem is to develop an ammetercircuit wherein changes in deflection angle 0 are compensated to vary inopposition to changes in the transistor 13 current i so that theresultant deflection angle of movement 21 accurately indicates thedesired function. The primary object of the invention is achieved byproviding a specific ammeter which performs .the sensitivity change tan0=d0/dT such that the current value (i) necessary for full scaledeflection at any expected environmental temperature coincides with thatshown, for example, in curve A of FIG. 3.

By using a shunt resistor having a low negative coefficient in parallelwith the moving coil 18, and ferrite magnet element 19 having a 'highnegative temperature coefficient, an ammeter circuit is provided tocorrespond to all values of output current in the transistor 13 stage inwhich coil 18 is connected regardless of ambient temperature variations.

The component values are carefully selected so that the specific ammeterof the invention satisfies the relative design relation Since ED R...)

is equal to approximately 1, the relation (1) can be simplified to whichforms a design equation compatible with values which can be chosenfreely from i i to i i in the relation of coil current i vs. shuntcurrent i As can be seen from the above mentioned relative Equation 2, alow cost magnet such as a ferrite magnet cannot be used in aconventional instrument for the present indicating function due to themagnet high negative temperature coefficient, on the order of 0.00l9/ C.In the present circuit, however, inexpensive ferrite magnet elements 19are successfully utilized because of the compensating effect achievedthereby with regard to the temperature characteristics of transistor 13.Any discrepancy in the characteristics of the deflection angle ofmovement 21 as a function of temperature which is not compensated by thetemperature characteristics of transistor 13 is compensated by shuntresistor 22, having a relatively low negative temperature coefficient.The establishment of a temperature gradient is possible even without ashunt resistor by designing the ammeter so as to satisfy the relativeequation Throughout the environmental temperature range of at least 0 to50 C., the specific ammeter design of this invention performs anindication similar to that shown in the room temperature condition (25C.) curve A in FIG. 3.

Including the above design considerations with respect to the ammeter,it should be possible to include a battery power level indicating meterin any transistor circuit, radio or otherwise, and be able to obtainsatisfactory compatibility.

What is claimed is:

1. A battery powered portable transistor radio receiver comprising anLP. stage, said stage including a transistor having an emitter collectorpath with a response having a positive slope of current versustemperature, a DC. ammeter having a coil connected in the emittercollector path of said transistor to provide selective indications ofthe condition of the battery and whether the receiver is tuned, saidbattery condition indication being derived while the receiver isdetuned, said ammeter also including a magnet and a movement, saidmagnet and coil being responsive to said current to deflect saidmovement with a response having a relatively large negative slope ofdeflection an-gle versus temperature, a resistor having a relatively lownegative temperature coeflicient connected in shunt with said coil, thesnegative temperature coefficient and said slopes being selected so thatthe deflection of the ammeter movement is relatively independent ofreceiver temperature.

2. The receiver of claim 1 wherein said magnet is of the ferrite type.

3. The receiver of claim 1 wherein the deflection angle, 0, of saidmovement is expressed as:

where: i is the current flowing through the shunt resistor; R is theresistance value of the coil at 0 C.; R is the resistance value of theshunt resistor at 0 C.; 'y is the relatively large negative slope; and Bis the temperature coefficient of said resistor.

4. The receiver of claim 1 wherein the deflection angle, 0, of saidmovement is expressed as:

tan 0=i [a-B+ -v)] where: i is the current flowing through the shuntresistor; 'y is the relatively large negative slope; and p is thetemperature coeflicient of said resistor.

UNITED STATES PATENTS References Cited 2,159,240 5/1939 Wheeler 33431XM3,112,444 11/1963 Parker 324l05 KATHLEEN H. CLAFFY, Primary Examiner.

R. S. BELL, Assistant Examiner.

